a) Field of the Invention
This invention relates to a spindle motor for driving a hub on which a disk is loaded, and is applicable to various driving apparatus for, for example, a hard disk, optical disk, and other disks, a polygon mirror driving apparatus, and the like.
b) Description of the Related Art
Driving apparatus for various disks and polygon mirrors drive a hub loaded with a disk, using a spindle motor; however, particles generated in the spindle motor may flow outside of the motor, attaching to the surface of the disk, affecting the functions of the disk such as writing and reading of signals and being a medium for optical reflection, and worse, damaging a playback head. There are spindle motors having labyrinth structures in which small air paths are provided at the top and bottom of the motor and between a rotary member and a fixed member, and are curved multiple times in order to prevent particles generated in the spindle motor from flowing outside of the motor. Japanese Utility Model No. H07-26962 and Japanese Utility Model No. H06-36374 disclose the example of the kind.
In recent years, as high speed and high capacity magnetic disk drives have become common and the reduction of particles generated in the spindle motor is a must, the required level of reduction has become so stringent that the conventional labyrinth structure is not able to fulfill the demand. Particularly when the working temperature for a motor is set to, for example, between 0.degree. C. and 55.degree. C., at 55.degree. C., the highest temperature, oil mist of lubrication grease having about 0.1 .mu.m of particle size is generated at a bearing; therefore, the labyrinth structure in a conventional spindle motor does not fully prevent particles, not meeting the required level of particle prevention.
FIG. 1 of Japanese Utility Model No. H06-36374 discloses a method for preventing particles from contaminating the space where a disk is loaded, wherein the facing planes 32 and 33 are closely provided between a hub 25 on which a disk is loaded and a frame 21 rotatably supporting the hub; and spiral grooves 34 for generating the air flow directed toward the internal space of the motor when the hub rotates are formed on a holder section 30 between the facing planes.
However, the air flow generated in the motor is not constant; only generating an air flow toward the inside of the motor cannot completely prevent the air contaminated with oil mist and particles from flowing out outside of the motor, and it is difficult to reduce the particle contamination to meet the current level of requirement.